Isolation amplifiers are commonly used for providing electric power to electrical equipment while isolating the electrical equipment from direct connection to a power source. Typically, an oscillating electrical signal is inductively coupled to electrical equipment, such as through a transformer, to provide electrical energy to the electrical equipment. A feedback connection may be provided from the electrical equipment to the power source to control the amount of electrical energy being provided through the transformer.
For example, U.S. Pat. No. 4,667,144 to Jones et al. discloses a high frequency, high voltage MOSFET isolation amplifier in which variations in the input signal are corrected by providing feedback through a magnetic yoke load circuit.
U.S. Pat. No. 5,187,446 to Daly discloses a feedback isolation amplifier that also employs a separate isolation amplifier as part of a feedback circuit to compensate for variations in the input and output signals.
U.S. Pat. No. 3,896,366 to Onogi discloses an isolation transformer having primary and secondary windings in which the current in each of the windings is controlled by a variable impedance element. The variable impedance element forms a current limiter under control of an input signal. This patent also discloses providing current or voltage feedback from isolated load equipment to an input of a differential amplifier at the primary winding to control the current conducted through the windings.
U.S. Pat. No. 4,506,230 to Ashley-Rollman discloses an isolation circuit formed of an isolation amplifier having a primary winding and a pair of secondary windings. One of secondary windings provides feedback to an operational amplifier on the primary side of the isolation amplifier circuit for compensation.
U.S. Pat. No. 4,541,040 to Allfather discloses a power conversion system in which an isolation transformer couples the output of a power amplifier to a load. An indication of the load is provided to the power amplifier through a separate feedback path.